<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    .box{
        width:250px;
        height: 52px;
        padding: 15px 30px;
        border: 2px solid #ccc;
        border-radius: 16px;
        margin: 0 auto;
    }
    .box .count{
        width: 60px;
        color: #666;
        font-size: 280%;
        line-height: 50px;
        padding-left: 6px;
        margin-left: 5px;
        border: 1px solid #fff;
    }
    .box div{
        margin-left: 5px;
        float: left;
        width: 50px;
        height: 50px;
        border-radius: 50px;
        border: 1px solid #666;
    }
    .gray{
        background-color: #eee;
    }
    .red{
        background-color: red;
    }
    .yellow{
        background-color: yellow;
    }
    .green{
        background-color: green;
    }
    </style>
</head>
<body>
    <div class="box">
        <div id="red"></div><!--红灯-->
        <div id="yellow"></div><!--黄灯-->
        <div id="green"></div><!--绿灯-->
        <div id="count" class="count"></div><!--倒计时-->
        <script>
        var lamp={
            red:{//红灯相关数据
            obj:document.getElementById('red'),
            timeout:30,
            style:['red','gray','gray'],
            next:'green'
            },
            yellow:{//黄灯相关数据
            obj:document.getElementById('yellow'),
            timeout:5,
            style:['gray','yellow','gray'],
            next:'red'
            },
            green:{//绿灯相关数据
            obj:document.getElementById('green'),
            timeout:35,
            style:['gray','gray','green'],
            next:'yellow'
            },
            changeStyle(style){//设置信号背景色样式
            this.red.obj.className=style[0];
            this.yellow.obj.className=style[1];
            this.green.obj.className=style[2];
            }
        };
        var count={
            obj:document.getElementById('count'),//倒计时的元素对象
            change:function(num){
                this.obj.innerHTML=(num<10)?('0'+num):num;
            }
        };
        var now=lamp.green;//获取绿灯亮的相关数据
        var timeout=now.timeout;//获取绿灯亮灯的剩余时间
        lamp.changeStyle(now.style);//设置绿灯亮时，红绿灯背景颜色样式
        count.change(timeout);//设置绿灯亮灯的剩余时间
        setInterval(function(){
            if(--timeout<=0){//切换信号灯
                now=lamp[now.next];//获取下一个亮灯的信号灯的相关数据
                timeout=now.timeout;//获取信号灯的剩余时间
                lamp.changeStyle(now.style);//设置信号灯的背景色样式
            }
            count.change(timeout);//设置信号灯亮灯的剩余时间
        },1000)
        </script>
    </div>
</body>
</html>